The present invention relates to a recordable optical disk apparatus, and in particular to a laser drive integrated circuit for controlling a pulse-segmented laser drive waveform of multi-valued levels, or more in particular to a laser drive integrated circuit and an optical disk apparatus with the laser drive integrated circuit mounted thereon, in which the operation can be switched at high speed and high accuracy in keeping with various drive waveforms.
In recent years, an optical disk recording and reproduction system higher in density has been in demand. The basic principle of an optical disk lies in the on/off control in which the laser is radiated when recording data corresponding to xe2x80x9c1xe2x80x9d of information and the laser is not radiated when recording data corresponding to xe2x80x9c0xe2x80x9d of information.
The techniques now essential to meet this trend includes the single-beam overwrite technique (the recorded data is erased while recording new data with a single laser beam) and the technique called the write strategy in which the recording power is controlled by pulse segmentation into multi-valued levels for controlling the recording mark shape to improve the density. These techniques increase the number of data input to the laser driver. A simple on/off control requires only one data. In a waveform requiring an intermediate level for overwrite operation or waveform control in which high-density marks are formed, however, the switching of a plurality of currents is required.
A conventional method, as disclosed in JP-A-8-147697, for example, has additional data for on/off control of intermediate power and requires a total of four current control systems. For the recent method of recording mark control for high density, the recording power level is controlled to three-valued or more levels and therefore the number of data is increased to four or five. To follow the future trend toward a still higher density, an even greater number of data are required.
In the future, a higher data transfer rate and a greater detail of segmentation of pulse width will be required for an increased number of power levels.
Also, an optical disk apparatus will be required to change the laser drive waveform adaptively in accordance with the recording/reproduction characteristic of the disk, to improve the data reliability by recording the data in an optimum drive waveform, and to make various disks recordable in keeping with various drive waveforms caused by different recording materials of the disk.
Normally, in an optical disk apparatus, a pickup makes up a movable unit and a signal control system constitutes a fixed unit. Also, a laser drive unit is arranged in the neighborhood of a laser diode mounted on the pickup. The portion from the signal control unit to the laser drive unit is wired using a flexible cable or the like. The flexible cable is used for transmission of the servo signal as well as the laser drive signal, and requires at least a length larger than the disk radius due to the fact that the pickup constitutes a movable unit.
In the above-mentioned prior art, an increased number of levels of waveform control leads to a correspondingly increased number of lines for laser drive control. This in turn increases the size of the flexible cable, thereby making it difficult to secure the space for accommodating the flexible cable. Another problem is a lengthened flexible cable laid about.
Also, a finer pulse segmentation for high-density recording increases the clock frequency for pulse segmentation control. An increased clock frequency with a lengthened flexible cable or a smaller width of each line leads to the problem of the distortion or delay of the transmission waveform, etc. This affects the pulse rise and fall rate, and the laser emission at the desired timing becomes impossible. Thus, the mark shape and the mark position accuracy are adversely affected, resulting in a data error.
Still another problem is the unrequired radiation from the cable which causes a noise.
In order to solve the above-mentioned problems, according to the present invention, there is provided a laser drive integrated circuit and an optical disk apparatus using such a circuit, comprising drive waveform information storage means for storing at least one information on the drive waveform for driving a laser diode in accordance with a binary recording signal recorded in a recording medium, a drive waveform decoder for decoding the drive waveform based on the information stored in the drive waveform information storage means, an address generator for selecting the drive waveform information of the drive waveform information storage means based on the binary recording signal recorded in the recording medium, and control means for causing the drive waveform information supplied from an external source to be stored in the drive waveform information storage means.